Why am I not being able of detecting a None value from a dictionary - json

Question

I have seen this issue many times happening to many people (here). I am still struggling trying to validate whether what my dictionary captures from a JSON is "None" or not but I still get the following error.
This code is supposed to call a CURL looking for the 'closed' value in the 'status' key until it finds it (or 10 times). When payment is done by means of a QR code, status changes from opened to closed.
status = (my_dict['elements'][0]['status'])
TypeError: 'NoneType' object is not subscriptable
Any clue of what am I doing wrong and how can I fix it?
Also, if I run the part of the script that calls the JSON standalone, it executes smoothly everytime. Is it anything in the code that could be affecting the CURL execution?
By the way, I have started programming 1 week ago so please excuse me if I mix concepts or say something that lacks of common sense.
I have tried to validate the IF with "is not" instead of "!=" and also with "None" instead of "".
def show_qr():
reference_json = reference.replace(' ','%20') #replaces "space" with %20 for CURL assembly
url = "https://api.mercadopago.com/merchant_orders?external_reference=" + reference_json #CURL URL concatenate
headers = CaseInsensitiveDict()
headers["Authorization"] = "Bearer MY_TOKEN"
pygame.init()
ventana = pygame.display.set_mode(window_resolution,pygame.FULLSCREEN) #screen settings
producto = pygame.image.load("qrcode001.png") #Qr image load
producto = pygame.transform.scale(producto, [640,480]) #Qr size
trials = 0 #sets while loop variable start value
status = "undefined" #defines "status" variable
while status != "closed" and trials<10: #to repeat the loop until "status" value = "closed"
ventana.blit(producto, (448,192)) #QR code position setting
pygame.display.update() #
response = requests.request("GET", url, headers=headers) #makes CURL GET
lag = 0.5 #creates an incremental 0.5 seconds everytime return value is None
sleep(lag) #
json_data = (response.text) #Captures JSON response as text
my_dict = json.loads(json_data) #creates a dictionary with JSON data
if json_data != "": #Checks if json_data is None
status = (my_dict['elements'][0]['status']) #If json_data is not none, asigns 'status' key to "status" variable
else:
lag = lag + 0.5 #increments lag
trials = trials + 1 #increments loop variable
sleep (5) #time to avoid being banned from server.
print (trials)

Answer 1

From your original encountered error, it's not clear what the issue is. The problem is that basically any part of that statement can result in a TypeError being raised as the evaluated part is a None. For example, given my_dict['elements'][0]['status'] this can fail if my_dict is None, or also if my_dict['elements'] is None.
I would try inserting breakpoints to better assist with debugging the cause. another solution that might help would be to wrap each part of the statement in a try-catch block as below:
my_dict = None
try:
elements = my_dict['elements']
except TypeError as e:
print('It possible that my_dict maybe None.')
print('Error:', e)
else:
try:
ele = elements[0]
except TypeError as e:
print('It possible that elements maybe None.')
print('Error:', e)
else:
try:
status = ele['status']
except TypeError as e:
print('It possible that first element maybe None.')
print('Error:', e)
else:
print('Got the status successfully:', status)